Thermochemical behavior of three sulfates (CaSO4, K2SO4 and Na2SO4) blended with cement raw materials (CaO-SiO2-Al2O3-Fe2O3) at high temperature

• Published in: Journal of analytical and applied pyrolysis 2019-09, Vol.142, p.104617, Article 104617
• Main Authors: Wang, Zean, Yang, Wei, Liu, Hao, Jin, Hu, Chen, Huiqin, Su, Kai, Tu, Yaojie, Wang, Wenlong
• Format: Article
• Language: English
• Subjects: Cement raw materials; Solid-phase reaction; Sulfate; Thermal decomposition
• ISSN: 0165-2370; 1873-250X
• DOI: 10.1016/j.jaap.2019.05.006

•K2SO4 has better thermal stability and lower reactivity in comparison with CaSO4 or Na2SO4.•C4A3S- can be found in both CSAF-CaSO4 and CSAF-Na2SO4 system at 1250 °C and 1150 °C respectively.•NC3S2 is generated by the reactions among CS, C2S and the decomposition product of Na2SO4 in CSAF-Na2SO4 system, inhibiting the formation of C3S in the clinker. Thermal behavior of three pure sulfates (CaSO4, K2SO4 and Na2SO4) as well as solid-phase reactions between each sulfate and cement raw materials (CaO-SiO2-Al2O3-Fe2O3, CSAF) at high temperature were investigated experimentally. As the results, K2SO4 is much more thermally stable and less reactive than CaSO4 and Na2SO4 in the CSAF system, moreover, CaSO4 and Na2SO4 can facilitate the formation of 2CaO·SiO2 (C2S) and reduce eutectic temperature of cement raw materials by 100 °C. CaSO4 can react with Al2O3 and CaO to form the mineral 3CaO·3Al2O3·CaSO4 (C4A3S-) at 1250 °C, while the formation temperature is decreased to 1150 °C in the CSAF-Na2SO4 system. For CSAF-K2SO4 system, the decomposition rate is very slow at low temperature, and K2SO4 can react with Al2O3 to form K3AlO3 at high temperature. For CSAF-Na2SO4 system, Na2SO4 can be easily melted to liquid phase, and react with CaO·SiO2 (CS) and C2S to generate Na2O·3CaO·2SiO2 (NC3S2) in the CSAF system, then inhibit the formation of 3CaO·SiO2 (C3S) in the clinker.